The proposed research concerns the temporal course of perception and retrieval for verbal information stored in memory. The planned experiments will systematically vary stimulus and task parameters in order to test theoretical assumptions about the nature of perceptual and mnemonic processing abilities in human beings. Subjects will memorize and retrieve visual and auditory displays of verbal material. Reading times and monitoring response times will be scored during the presentation. Retrieval latencies and rates as well as item and order errors will be scored from the retrieval data. Experiments on the temporal course of perception are concerned with the following problems: (a) What is the number of stages of perceptual processing and the nature and limitations of processing at each stage? (b) What is the amount or duration of coding and the form of the internal stimulus representation at each stage? Experiments on the temporal course of retrieval are concerned with the following problems. How does the rate and strategy of searching memory depend on (a) the nature and number of items, (b) their structural organization, (c) the semantic relationships among the items, and (d) the linguistic requirements of the retrieval task itself. These problems have been formulated in terms of mathematical models that can be tested against the empirical data obtained. This research has implications for improving reading abilities in normal adults and children, and for understanding linguistic and mnemonic abilities that are affected in various types of brain damage and in mental retardation.